Onboard control computers have become prevalent in motor vehicles, but as safety, economy, and emissions requirements have continued to escalate, friction braking systems, and traction control devices have proven below the requirements set out in government regulations and the implicit demands of competitors' achievements. Successive generations of onboard control computers have acquired increasing data sensing and retention capability as the electronics have advanced.
Present external diagnostic and display apparatus, known as diagnostic tools, are commonly limited to reporting the data acquired by the onboard control computer itself. Increasingly, subtle subsystem failures in vehicles overload the ability of maintenance technicians, not simply to read the faults detected and stored by the diagnostic tools themselves, but to combine those readings with peripheral measurements and deduce corrective actions with both speed and accuracy.
Currently in the automotive industry, there are both stand alone and hand-held diagnostic testers or tools used in connection with motor vehicle maintenance and repair. For example, hand-held diagnostic tools have been used to trouble-shoot faults associated with vehicular control units. Diagnostic tools detect faults based on Diagnostic Trouble Codes or DTCs that are set in the vehicle's onboard computer. A DTC can be triggered and stored when there is a problem with the vehicle. A technician then retrieves the DTC using a diagnostic tool, repairs the associated problem and then deletes the DTC from the vehicle's computer.
However, problems in diagnosing the cause of failure in a vehicle can occur with a vehicle where a DTC is not set. In this instance, a technician is left to his or her own expertise to troubleshoot the problem. There can be an instance when the vehicles have drivability problems and no DTCs are stored in the vehicle's computers. Diagnosing the problem is difficult for the technician when no DTC is stored in the vehicle's computer. The technician then must use inefficient measures of using technical service bulletins (i.e., TSB's), diagnose based on symptoms charts, talking with others with regard to the problem, or merely guessing.
Accordingly, it is desirable to provide a method and apparatus that will allow a technician to use a diagnostic tool to determine the nature of a problem where no DTCs have been triggered.